1. Field of the Invention
This invention relates generally to safety ski bindings, and more particularly to safety ski bindings which release the ski boot from the ski when a force between the boot and the binding displaces the binding a certain distance relative to the ski in one or both of two directions which are perpendicular to each other.
2. Description of the Prior Art
The attributes of a well designed ski binding are well known in the prior art. Such bindings should provide a firm connection between the ski and the boot for skiing purposes, and should positively and reliably release the boot from the ski before injury causing levels of forces and/or moments are reached. Although positive and reliable release of the ski binding is an extremely important attribute, the ski binding should be capable of experiencing some relative motion with respect to the ski without releasing. This will prevent premature and undesirable release of the binding due to short duration shocks which are normally encountered during skiing.
In many cases the force imposed upon a ski binding will be a combination of a normal force resulting from a forward fall, and a transverse force resulting from a twisting, or torsional motion of the skier's body relative to the ski. Although the individual normal and transverse components of force may not be sufficiently high to cause an injury to a skier, the resultant force may be of an injury causing magnitude. Accordingly, it is highly desirable to design ski bindings so that they will reliably release when the resultant of several different forces imposed upon the binding reaches an injury causing level. Stating this another way, a well designed ski binding reacts to resultant forces, as well as to individual forces.
The most common safety ski bindings utilized today retain the ski boot to the ski at both the toe and the heel of the boot sole. The heel part of the binding most commonly includes a generally V-shape retaining clip which engages the upper surface of the sole, and releases the connection between the sole and the ski when a positive normal force imposed upon the retaining clip, as for instance in a forward fall, exceeds a certain preset level.
The toe part of the binding generally includes boot retaining sections which are rotatable about an axis which is normal to the boot supporting surface of the ski. These retaining sections release the toe of the boot when a torsional moment about an axis generally parallel to the upper surface of the ski exceeds a certain preset level. Toe bindings of the above-described type often require the boot to slide relative to the ski and/or the toe binding to actuate the toe binding for releasing the boot from the ski. The force required to affect this sliding motion is a function of the frictional resistance between the sliding surfaces. Unpredictable variations in frictional resistance exist because of dynamic or inertial forces which occur during skiing. Unpredictable variations in frictional resistance also occur as a result of the presence of dirt, snow and ice between the sliding surfaces. Moreover, temperature variations cause unpredictable variations in the frictional resistance between the sliding surfaces. In view of these unpredictable variations in frictional resistance the force required for laterally displacing the toe retaining part of the binding to release the boot is highly unpredictable.
A skier's weight is most often on the ball of his feet, and this creates a high normal force near the toe-retaining part of the binding. This results in high coulomb friction between the ski boot and ski. This high coulomb friction tends to resist the sliding action of the boot relative to the ski, and this resistance adversely affects the reliability of the release action of the toe binding during a twisting fall of the skier.
From the above discussion it should be apparent that the most desirable type of ski binding is one in which a sliding of the ski boot relative to the binding and to the ski is not relied upon to effect separation of the boot from the binding. Moreover, it is most desirable to provide the heel binding with a release mechanism which is responsive to excessive torsional forces creating a moment about an axis normal to the upper surface of the ski. Since a skier's weight is generally on the ball of his feet during skiing, the normal force imposed upon the ski by the boot is generally lowest at the heel. Accordingly, the frictional resistance to sliding motion between the ski boot and the ski is also generally lowest at the heel of the boot, and for that reason, it is most desirable to provide the release mechanism responsive to excessive torsional forces in the heel retaining part of the ski binding.
U.S. Pat. No. 3,620,545, issued to Korger on Nov. 16, 1971, relates to a ski binding safety clamp which engages a sole of a ski boot at its heel. The ski binding has a control mechanism for releasing the clamp from the boot when the upward normal forces and/or horizontal forces imposed upon the clamp exceed a preset level. The preset force level at which the clamp releases the boot is controlled by a single spring member. Accordingly, the preset force at which the safety clamp will release cannot be independently set for different types of forces imposed upon the clamp. Stating this another way, once the spring is set to provide a predetermined load at which the safety clamp will release during a forward fall of the skier, the load at which the safety clamp will release during a torsional fall, or a comined forward and torsional fall, is automatically determined. Accordingly, the Korger ski binding does not provide the skier with any latitude to independently setting the force levels at which the safety clamp will release under different types of load conditions.
The safety clamp of the Korger binding is retained in a boot clamping position by the engagement of cam surfaces on a catch support and a catch member. When the force upon the safety clamp exceeds a preset level the clamp will be moved to cause the cam surfaces of the catch support and catch member to slide relative to each other into a position in which the catch support disengages the catch member to permit a positive release of the safety clamp from the boot. This type of release mechanism requires fairly complicated cam designs to provide for the release of the catch member when either excessive horizontal forces or excessive normal forces are imposed upon the clamp. Moreover the construction of the Korger binding is such that the spring induced forces which resists the release of the safety clamp always acts through the camming surfaces of the catch support and the catch member. This creates undesirable friction of the camming surfaces caused by their sliding over each other and thus the release action will be adversely affected. In the event that a cam surface becomes slightly distorted because of this sliding action, the reliability of the release action of the safety clamp will be adversely affected.
It is known to provide a toggle link arrangement for retaining a safety clamp in a locked position against the sole of the ski boot, and for positively releasing the safety clamp when an excessive force is imposed upon it by the ski boot. Representative ski bindings employing toggle link arrangements are disclosed in U.S. Pat. Nos. 3,529,846, issued to Voster, and 3,550,996, issued to Marker. In these prior art ski bindings the safety clamp is rotatable about an axis disposed transversely to the length of the ski for both clamping and releasing the ski boot. Ski bindings employing a toggle link arrangement provide an extremely reliable release action of the safety clamp. However, prior art bindings employing a toggle link arrangement have been responsive only to upward normal forces imposed upon the clamp. In other words, when the clamp is employed to retain the heel of a ski boot against the ski, it is only designed to release when a positive normal force upon the clamp exceeds a certain level. The prior art safety clamps employing toggle link arrangements have not been designed to release upon the application of transverse forces to the clamp.
It is highly desirable to provide a ski binding with a safety clamp that is releasable from a ski boot by a toggle link arrangement, and which will be released by the toggle link arrangement when a torque in either one or both of two directions which are perpendicular to each other exceeds a preset level, and thereby all sliding of the different elements of the binding over each other has been eliminated. It is to this type of ski binding that the instant invention relates.